Electrical transformer



Nov. 25, 1924. 1,516,519

G.CmSSON ELECTRI CAL TRANS FORMER Filed Dec. 14. 1923 I N VE N TOR 61 674515 5011/ fiy A TTORNE Y Patented Nov. 25, 1924.

UNITED STATES PATENT OFFICE.

GEORGE CRISSON, OF HACKENSACK, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

ELECTRICAL TRANSFORMER.

Application filed December 14, 1923.

To all whom it may concern.

Be it known that I. GEORGE GRISSON, residing at Hackensack, in the county of Bergen and State of New Jersey, have invented certain Improvements in Electrical T ransformers, of which the following is a specification.

This invention relates to electrical transformers and particularly to means for preventing a transfer of energy between two circuits, each connected with a primary winding of a transformer, the secondary windings of both transformers being connected in series to a circuit of very high impedance.

In the operation of telephone circuits having repeaters connected therewith, it is frequently desirable to monitor the service upon such circuits. Such repeaters are normally of the two-way type. If a telephone receiver were bridged across the telephone line at one side of the repeater, the current entering the receiver from one direction would be unamplified while that from the other direction would the amplified. Such monitoring service is, of course, unsatisfactory and consequently the monitoring leads are connected across the line circuit at each side of the repeater so that the currents fiowing through the receiver from each direction are amplified. If these monitoring leads were connected to the receiver through separate transformers, the secondaries of which are connected with the receiver, such secondary circuit would form a coupling between the monitoring leads and singing would result. In order to prevent this undesirable elfect, a vacuum tube has been used in the secondary circuit to open the secondary circuit and thus to break the coupling between the monitoring leads. It has been found, however, that this does not entirely prevent the transfer of energy between the monitoring leads, because the capacity between the primary and secondary windings created a circuit whereby some of the energy would be inductively fed back from the secondary to one of the primary circuits.

It is the object of this invention to provide means whereby the capacity of the windings of such transformers is prevented from establishing a circuit which will pro duce a feeding back of energy between the secondary and the primary circuits.

This invention will be clearly understood Serial No. 680,727.

from the following description when read in connection with the attached drawings of which Figure 1 shows one type of circuit in which the invention is embodied, and Fig. 2 shows upon a larger scale a portion of the circuit of Fig. 1 relating to the transformers per so.

In Fig. 1, a telephone line or other signaling circuit is represented by a pair 1 of conductors extending in one direction from the telephone repeater and by the conductors of pair 2 extending in the opposite direction. Pair 1 is connected with the windings 3 of a hybrid coil which also has connected therewith a balancing network at designed and adjusted to balance the pair 1. In similar manner pair 2 is connected with the windings 5 of another hybrid coil having a balancing network 6 connected therewith to balance pair 2. An amplifier 8 which may be of any type, transmits in the direction represented by the arrow, and is connected with the windings 3 by means of the circuit 7. The output side of this amplifier is connected by circuit 9 with the winding 10 of the hybrid coil with which windings 5 are also connected. In similar manner the amplifier 12, which transmits in the direction represented by the arrow associated therewith, is connected by circuit 11 with the windings 5, and the output side of this amplifier is connected by circuit 13 with the winding lat of the other hybrid coil. The monitoring leads 15 and 18 are connected with pairs 1 and 2 respectively at each side of the telephone repeater. Lead 15 is connected with the primary winding 16 of the transformer 17. In similar manner lead 18 is connected with the primary winding 19 of transformer 17. The secondary windings 20 and 21, of transformers 17 and 17 respectively, are connected in series in the input side of the vacuum tube 22, in series with the filament and grid of the said tube. The output side of this tube is connected with the primary winding 23 of the transformer 24, the secondary winding 25 of which is connected with a telephone receiver 26 In the operation of the circuit shown in this figure, voice currents set up in circuit 1 by apparatus connected with the distant end thereof will be impressed by the hybrid coil upon circuit 7 and will be amplified by the device 8. The amplified currents will be impressed upon the windiuc' 10 and will be induced in the winding "i of that hybrid coil in such manner as to how over the circuit 2 but not into the ci cuit 11 ct d with the amplifier." ln like n'ninncig. currents set up in circuit 2 by a n aratus connected with the distant end the i will be impressed upon circuit 11 so as to be ainpli lied by the device 12, and the ,ltant azuplilied currents will flow throi the winding i l of the hybrid coil connected with line 1 These currents will not howei pass into the circuit 2'' connected with amplifier 8 so that singing; will be prevented.

Eliice the leads 15 and 18 are connected across the circuit 1 and 2 respectively, the currents flowing in the latter circuits will also cause a flow of current through the respective leads, viz, there will llow through the lead 15 not only the unanipliiied current set up in circuit 1 by the apparatus connected with the distant end thereof, but also the current amplified by 12 and impressed upon circuit 1 by the hybrid coil comprising the windings 3 and 14:. in similar manner there will be set up in the lead 18 the unainpliiied current Flowing in circuit 2 and also the current au'uoli'lied by 8 and impressed upon the circuit 2 by the hybrid coil comprising the windings 5 and 10. 'llhe currents flowing through the lead 15 and the winding 16 of transformer 17 will induce a potential in winding 20 and similarly the currents flowing through lead 18 and winding}; 19 of transformer 17 will induce a potential in winding 21. Since the unainplilied current tlowing in one ot the loads is the same signal current as the amplified current in the other lead and ditlers thereiroin only in magnitude, and since both currents are impressed upon the monitoring circuit at substantially the same instant of time, it is oi. no practical importance to consider the e'l'lect oil? the unan'lplilied current, and consequently further reference thereto will not be made in describing}; the invention. Since the circuit containing the windings 20 and 21. is open. by virtue ot the approximately infinite impedance oi the space between the grid and the lilau'ient ot the tube 22, no current will flow in this circuit and consequently there will be no transfer of energy between the circuit 15 and '18 by \irtue oi? the coupling through the conunon secondary circuit it the etl'cct of distributed capacity between the windings 19 and 21 could be eliminated. It has been t'ound that since the filament oi"? the vacuum tube is grounded, or has an admittance to ground, and since the circuit 18 has also an admittance to ground, the establislnnent off a potential across the winding 20 will cause current to flow from ground throrurh the said winding and through part oi the winding 21 and through the distributed. capacity heeuro tween winding 21. and winding l9 thence over the conductors or circuit 18 and through the admittance thereoi to ground. This will be seen clearly in Fig. 2. llhecurrent that flows throgh the distributed capacity between the windings 19 and 21 also flows through a number of the turns ot the winding 21 thereby inducing a difference oi potential in the winding 19 which causes an interfering current to flow in circuit 18.

lilly invention consists in inserting a shield 28 between the windings 1S) and L1 that the mutual capacity between the windings is eliu'iinated though capacity between each winding and the shield still exists. It will be seen, therefore, that when a diil 'erence of potential is set up in winding 20 by current flowing through winding 16 current will flow from ground (or through the ad-- niittancc to ground) to the filament thence through winding; 20 to point 27, thence through. the shield 28 and the capacity to winding 19, thence over the conductors o'l. circuit 18 and through the admittance ot such conductors to ground We current will flow through any oi the turns of winding 21, and consequently no current will, be induced in winding 19 so that interference between circuit 15 and 18 is thereby avoided. ln similar manner the creation o'l crosstalk in the circuit 15 when current is flowing); through circuit 18 may be avoided. it will be readily seen that any current [lowing through circuit 18 and through winding 19 will induce a potential across the winding 21. It the shield 28 were not present current would flow as the result of this potential across the winding :21 over a circuit from ground, through winding); 20 and part of winding 21, thence through the distributed capacity to winding 19 and over the conductors oil? circuit 18 and through the admittance 01? these conductors 1o ground. The current flowing through the winding 20 will. off course induce a potential across winding 16 and set up cross-tall; in circuit This cross-tall: is prevented by the use of the shield 28 connected to the midpoint 27 between the windings 20 and 21 in the following manner. The induced potential in winding 21 will cause the current to tlow through a local circuit including a part or all of the winding: 21, the distributed capacity to the shield 28 and the connection between the shield and the winding" 21 at the point 2". will acmrdingly be seen that the presence ot this shield localizes the current flow resulting; from the induced potential. in winding 21 and thereby prevents a flow of current through winding 20 thus preventing; the setting up of interference in circuit 15.

lVhile this invention has been shown as embodied in a particular form and. arrangement or parts, it is not limited to this pan all ticular form but is capable of embodiment in other and different forms without depart-- ing from the spirit and scope of the ap pended claims.

\Vhat is claimed is:

l. The combination with two transformers each having a primary and a secondary windin of two input circuits each connected with a primary winding of a transformer, the secondary windings of both transformers being connected in series with the grid and filament of a vacuum tube, and a shield interposed between the primary and secondary windings of one transformer and connected with the midpoint between the said secondary windings.

2. The combination with two transformers, each having primary and secondary windings, the secondary windings being connected in series, one of said transformers having a shield between its windings connected with the junction of the secondary windings, of two input circuits individual to and connected with the said primary windings, a multi-electrode vacuum tube having its grid and filament connected with the said serially connected secondary windings, and a current indicating device connected with the plate and filament of the said vacuum tube.

3. The combination with a circuit having a source of potential connected therewith, of a second circuit, a third circuit of very high impedance inductively coupled with each of said other circuits, the said third circuit being normally open through a non-conductive gap, and a shield interposed between the windings of the inductive coupling between the said second and said third circuit and so connected with the windings of the said third circuit as to prevent reaction between the lirst and second circuits.

at. The combination with a signaling circuit of a two-way repeater inserted in said signaling circuit, and a monitoring circuit, connected with said signaling circuit at each side of said repeater, including two transformers having their secondary windings connected in series with a unilateral translating device, one of said transformers having a shield between its primary and secondary windings connected with the junction of the secondary windings of both transformers.

The combination with a repeater having oppositely transn'iitting paths of a monitoring circuit, connected with each end of said repeater, having two transformers connected therewith, the output side of said transformers being connected in series with a common circuit of very high impedance, and one of said transformers having means to prevent the induction of current in its primary winding by current flowing through its secondary winding as the result of capacity between the said windings.

(3. 1n a monitoring circuit, the combination with two input circuits of two transformers individual to the input circuits, each having a primary and a secondary winding, a vacuum tube having its input side connected with said secondary windings in series, a. receiver connected with the output side of said vacuum tubes, one of said transformers having a shield between its windings connected with the junction of the secondary windings of both transfoiners.

7. The combination with two transformers, each having a primary and a secondary winding, of a circuit of very high impedance grounded either conductively or through admittance, the secondary windings of both transformers being serially connected in said circuit of high impedance, a second and a third circuit, each connected with a primary winding of said transformers, and a shield interposed between the windings of that transformer whose second ary winding is more remote from the grounding point of said first circuit, the said shield being connected with the junction point of said secondary windings.

8. The combination with two transformers, each having a primary and a secondary winding, of a circuit having a vacuum tube therein, the filament of which is grounded, the secondary windings of both transformers being connected in series with each other and both in series with the grid and filament of said vacuum tube, input circuits individual to and connected with the primary windings of said transformers and a shield connected between the windings of that transformer whose secondary winding is connected directly with the said grid, the said shield being connected with the junction point of the said secondary windings.

In testimony whereof, I have signed my name to this specification this 13th day of December 1928.

GEORGE ORISSON. 

